The goal of this Phase I work is to finish development of an innovative interactive app designed to help patients appropriately use total knee replacement (TKR) surgery and provide support to achieve best outcomes. TKR is highly effective for treating advanced osteoarthritis of the knee, but it has risks. Appropriate use can be assured by engaging patients in a Shared Decision Making (SDM) process to help them fully understand risks and benefits of different treatments. Decision aids typically present average benefits and risks, without personalizing information for unique patient features that may influence outcomes. Currently, there is no valid tool for individualizing prognosis following TKR. Furthermore, implementing SDM is difficult in the dynamic, fast-moving, stressful clinic environment of face-to-face visits with surgeons. Mobile technologies offer a potential solution. We are developing a mobile and web application that has interactive features and communication tools to empower patients considering knee replacement surgery. The App uses validated Patient Reported Outcome (PRO) measures to present time trends for health status measures such as pain and function. It provides reference values for these scores so patients can gauge how they are doing compared to others. By answering a few questions about age, sex, weight, height, and health status measured by PROs, patients can see how they compare to adults in the Unites States and TKR patients similar to them. These comparisons may help them decide if surgery is right for them. Patients have the option to share PRO data with their providers. The App leverages validated prediction models that present individualized prognosis for key outcomes. Patients can see personalized estimates of predicted physical function and pain following surgery, and other outcomes such as risk of infection, readmission and repeat surgery. By dialing in changes for modifiable risk factors (such as weight, tobacco/alcohol use, and baseline physical function score), patients can see the potential impact of these lifestyle changes on outcomes. We have developed a prototype that solves the technological challenges for HIPAA compliance, secure communication, identity validation, and sharing PROs with one electronic health record. However, usability tests showed that patients found it difficult to navigate features independently and understand PRO scores. We propose to redesign the user experience and user interface in Phase I such that patients can directly track their outcomes over time, and leverage standardized PRO score presentation methods developed by the NIH PROMIS program?s Computerized Adaptive Testing (CAT) to clearly present PRO scores. Improved usability will prepare the App for market and examining real world use by patients going through the TKR treatment journey. The technology will then be ready for assessment of its impact on patient experience and outcomes, and the hypothesis that convenient, personalized support motivates more appropriate use, better experience, and better outcomes for TKR.